Method of making photo-printing plates



y 1, 1956 A. T. WICKLUND 2,757,087

METHOD OF MAKING PHOTO-PRINTING PLATES Filed April 2, 1953 IN V EN TOR. /4?/ 0Afl fliim za/vp United States Patent METHOD OF MAKING PHOTO-PRINTING PLATES Arnold T. Wicklund, St. Paul, Minn., asisgnor to Buckbee- IVIears Company, St. Paul, Minn., a corporation of Minnesota Application April 2, 1953, Serial No. 346,426

4 Claims. (Cl. 955) This invention relates to the manufacture of printing plates for use in the manufacture of precision articles formed with a multiplicity of minute perforations of predetermined geometric shapes, sizes and arrangement or having surface coatings defining dots or transparent areas of minute sizes and predetermined shapes, sizes and relative positions or groupings. Examples of such precision articles are the aperture masks and plates carrying phosphor dot arrays used as component parts of tri-color television tubes and certain printing surfaces.

It is an object of my invention to provide a novel method for making such printing plates whereby improved accuracy, uniformity and control of the shape, location and size of the minute figures defined by the images on the plates is obtained.

A particular object is to make such improved printing plates by procedure which includes the steps of preparing a plurality of identical prints each bearing the image of a basic design to be reproduced, superimposing the several prints one on another and adjusting them manually in predetermined relative positions to form a composite design from the group of basic designs and thereafter reproducing the composite design on a printing plate by contact printing procedure.

The invention also includes certain novel techniques and procedures which will be more fully pointed out in the following specification and claims.

Referring to the accompanying drawing which illustrates, by way of example and not for the purpose of limitation, typical basic designs and certain composite designs which may be formed therefrom by contact printing procedure according to my invention:

Figure 1 is a diagrammatic fragmentary plan view showing, greatly enlarged, a ruled glass plate upon which a basic design is defined by opaque lines;

Fig. 2 illustrates diagrammatically a print bearing the image of a composite of two of the basic designs;

Fig. 3 shows a finished plate which is a composite of three of the basic designs, and

4 shows a fragmentary portion of a composite design suitable for use in the formation of certain etched printing surfaces.

In Fig. 1 a flat transparent plate is indicated by the numeral 4 and spaced parallel, opaque lines constituting what may be termed the basic design are indicated by the numeral 5. These lines are clear cut, of uniform width and spaced apart precisely in accordance with the basic design required. They may be formed mechanically by the use of a precision ruling machine and the grooves formed by the machine may be filled with an opaque substance as in the case of ruled plates for use in making half-tone screens for photo-engraving purposes.

According to my preferred procedure such a ruled glass plate having a multiplicity of opaque, parallel lines of predetermined width and spaced apart precisely according to a predetermined design may be used to make three identical prints on thin base photographic film. For

2,757,087 Patented July 31, 1956 some designs positive prints of the basic design may be required and the procedure may include the making of one or more negatives from the ruled glass plate and the use of a negative to make three identical positives of the basic design by contact printing. These prints may be made by simultaneous exposure in a contact printing frame using a vacuum to insure uniform contact between the surfaces of the several film layers and the ruled glass plate, or with a negative print made therefrom. Thereafter the three prints are developed and dried.

As the next step in my preferred method, one of these prints is suitably supported on the top surface of a light table having a translucent top through which light passes from below to illuminate the work supported on the top. To facilitate handling, the film may be fastened to a glass plate and the plate may be supported in convenient position on the table. The other two prints of the basic design are then superimposed one on another and placed in overlapping relation to the first print which has been positioned on the light table. Then, by relative movement and rotation of the several prints, manually, in contact one with another, the images of the lines on the respective prints are placed at the angles required to produce the composite design of the finished plate. For example, where a hexagon design, such as that illustrated in Pig. 3 of the drawing, is required on the finished plate, the line images of each of the thin prints are adjusted to extend at an angle of 60 degrees relative to the line images of each of the other two prints. While observing the composite design through a microscope, the operator adjusts the relative positions of the three prints until the required array of hexagonal figures of equal size and regular uniform shape appear as the composite design.

Thereupon, the topmost print is removed from the others and, while carefully retaining the other two in their adjusted relative positions, their margins are secured together, preferably by the use of a suitable cement or other adhesive. As the next step, a photographic contact print on glass having a light sensitive coating is made from the two prints secured together in their overlapping adjusted positions. This composite print is then developed and dried.

Fig. 2 of the drawing illustrates a fragment of this composite of two of the basic designs in positive form on a glass plate 6. A series of parallel lines 5a represent those which have been photographically reproduced from one of the prints of the lines 5 (Fig. 1) and a second series of parallel lines 55 represent those which have been similarly reproduced from the second print of the lines 5 after adjustment to cause the lines of one series to extend precisely at an angle of 60 degrees to those of the other series. A multiplicity of identical diamond shaped figures are thus formed. In case these figures are defined by opaque images it will be necessary as the next step to make a reverse print or positive of the negative print showing diamond shaped figures on a glass plate by a similar photographic procedure using a vacuum printing frame. This reverse print on glass is then developed and dried and placed on the light table. The third of the three positive prints on thin base film is then superimposed on the positive composite print showing diamond shaped figures defined by transparent areas, and the third print is readjusted thereon until the desired composite hexagonal design of transparent dots of equal size and in the required hexagonal array again appears by observation through a microscope from above. The desired effect is obtained when the lines of the third print extend precisely at 60 degrees to both series of lines of the composite print and in position to reduce the diamond shaped areas to equilateral regular hexagons.

The third print is then secured in place on the plate carrying the composite image and the resulting composite design is reproduced on a glass plate by contact printing procedure. For some purposes a negative plate of this character may be used as the final master but where a positive such as that shown in Fig. 3 is required a reverse print on glass is made. The resulting plate is a composite wherein the several groups of angularly disposed lines are opaque and the areas of the hexagonal dots are transparent.

In Fig. 3 the transparent plate is indicated at 7 and the several series of parallel lines reproduced from the three prints of the basic design are indicated respectively at 50, b and 5c. Throughout the procedure described herein, extremely accurate, full sea e reproductions are obtained by photo-printing wherein air is exhausted from the frame to retain the sensitized film or plate in overall contact with the print to be reproduced during exposure to actinic light. The plates produced as hereinbefore described are of unusually high quality.

In Fig. 4 I have shown, diagrammatically, a composite design on a fragment of a photo-printing plate for use in making etched depressions in printing surfaces, e. g., those used in rotogravure printing. The small translucent areas defined by the crossing opaque lines are of a shape best suited for the photo printed areas to be etched in the formation of depressions to receive the ink. This design is shown on a transparent plate 8 and is composed of a multiplicity of opaque lines 9 extending vertically and a multiplicity of similar lines 10 extending horizontally. Each of the lines 9 and 10 is formed with a succession of approximately elliptical enlargements in width and the vertically and horizontally extending lines are arranged to form transparent areas ll of uniform size and shape, each having four convex sides of equal length. This design is formed in a manner similar to that shown in Fig. 2 hereinbefore described, that is to say, by the use of a pair of identical prints of the basic design comprising a series of substantially parallel lines uniformly spaced and of required varying widths.

In the design of Fig. 4, as in that shown in Pig. 3, it is essential that one series or group of lines intersect those of another series precisely at predetermined points along the lines of both series. To obtain this result, the adjustment of the several basic design prints can best be performed manually while they are relatively movable, superimposed one on another and under microscopic observation. They are then secured together in their adjusted positions and then photo-printed by contaet printing in a vacuum frame, as hereinbefore described.

Where maximum uniformity and accuracy in the shape, location and size of the dot array is not required, it may be feasible to reproduce by contact printing procedure the final composite design from the three superimposed prints on thin film. However, it is di'llicult to eliminate undesirable optical elfects and resulting inaccuracies in the printing if it is attempted to photoprint in one operation from three or more superimposed prints. Such undesirable effeets are substantially eliminated by my preferred procedure, hereinbefore described, wherein a composite of two of the adjusted prints is reproduced on glass before proceeding to reproduce the adjusted third print as a part of the composite of all of them.

It will be evident that by varying the Widths and spacing of the lines of the basic design, the proportions of translucent areas to opaque areas of the composite design may be varied between wide limits. By this method it is feasible to reproduce fine line composite designs wherein the basic design has 1000 or more lines per inch and the corresponding number of dots per inch are reproduced in precise predetermined shapes and arrangements with great precision on the end or final plate.

Having described my invention, what I claim as new and desire to protect by Letters Patent is:

l. The method of making a photo-printing plate which comprises, preparing at least three prints on thin film material each bearing the image of a multiplicity of parallel lines, superimposing said prints one on another with the images of the lines angularly disposed one to another, manually adjusting the relative positions of the three superimposed prints to produce a composite design of polygonal figures of predetermined size and shape, removing one of said prints from the superimposed group of three prints, retaining the other two prints in their relative positions as so adjusted, making a developed composite photographic print from the two superimposed prints, superimposing the third print on said composite print of the other two prints, manually adjusting the position of the third print on the composite print to reproduce from the superimposed prints said composite design, and reproducing said last mentioned composite design on a light sensitive plate photo-mechanically.

2. The method of making a photo-printing plate which comprises, preparing three identical prints on thin film material each bearing the image of a multiplicity of parallel lines, superimposing said prints one on another with the images of the lines angularly disposed one to another, manually adjusting the relative positions of the three superimposed prints to produce a composite design of hexagonal figures of substantially uniform size and shape, securing two of the superimposed prints in said adjusted position, removing the third print, reproducing on a transparent plate and by contact printing and developing the composite design formed by the two prints secured in superimposed position, then making a developedreverse contact print from said plate, superimposing the third print on said reverse print and manually adjusting said third print thereon to produce a composite design consisting of a multiplicity of hexagonal figures of substantially equal size and reproducing said last mentioned composite design on a light sensitive plate photomechanically.

The method of making a photo-printing plate which comprises, preparing three identical prints on thin film material. each bearing the image of a multiplicity of parallel lines, then fastening one of said prints on a transparent supporting plate, superimposing the other two prints on the one so supported with the images of the lines angularly disposed one to another, manually ad- 'usting the relative positions of the three superimposed prints to produce a composite design of hexagonal figures of substantially uniform size, adhesively securing two of the superimposed prints in said adjusted position, remo ing the third print, reproducing on a transparent plate and by contact printing and developing the composite design formed by the two prints secured in superimposed position, then making a reverse developed contact print from said plate, uperimposing said third print on said reverse print and manually adjusting the third print thereon to produce a composite design consisting of a multiplicity of hexagonal figures of substantially equal size and reproducing said last mentioned composite design on a transparent plate photo-mechanically.

4. The method of reproducing on a photo-printing plate a composite design consisting of at least three series of crossing lines which comprises, preparing at least three substantially identical prints on thin photographic film, each bearing the image of a basic design comprising one series of said lines, superimposing said prints one on another with their designs angularly disposed one to another, manually adjusting the relative positions of said superimposed prints to produce a composite design consisting of a multiplicity of minute, equal areas of polygonal shape, removing one of said prints from the superimposed group of three prints, retaining the other two prints in their relative positions as so adjusted, making a developed composite photographic print from the two superimposed prints, superimposing the third print on said composite print of the other two prints, manually adjusting the position of the third print on the composite print to reproduce from the superimposed prints said composite design, and reproducing said composite design FOREIGN PATENTS photographically from the superimposed prints by con- 488 463 Great Britain July 7 1938 tact printing on a light sensitive plate.

OTHER REFERENCES References Cited in the file of this P 6 Smith: Tint Screens Process, Engravers Monthly,

UNITED STATES PATENTS January 1948, pages 10,

521,659 Levy June 19, 1894 

1. THE METHOD OF MAKING A PHOTO-PRINTING PLATE WHICH COMPRISES, PREPARING AT LEAST THREE PRINTS ON THIN FILM MATERIAL EACH BEARING THE IMAGE OF A MULTIPLICITY OF PARALLEL LINES, SUPERIMPOSING SAID PRINTS ONE ON ANOTHER WITH THE IMAGES OF THE LINES ANGULARLY DISPOSED ONE TO ANOTHER, MANUALLY ADJUSTING THE RELATIVE POSITIONS OF THE THREE SUPERIMPOSED PRINTS TO PRODUCE A COMPOSITE DESIGN OF POLYGONAL FIGURES OF PREDETERMINED SIZE AND SHAPE, REMOVING ONE OF SAID PRINTS FROM THE SUPERIMPOSED GROUP OF THREE PRINTS, RETAINING THE OTHER TWO PRINTS IN THEIR RELATIVE POSITIONS AS SO ADJUSTED, MAKING A DEVELOPED COMPOSITE PHOTOGRAPHIC PRINT FROM THE TWO SUPERIMPOSED PRINTS, SUPERIMPOSING THE THIRD PRINT ON SAID COMPOSITE PRINT OF THE OTHER TWO PRINTS, MANUALLY ADJUSTING THE POSITION OF THE THIRD PRINT ON THE COMPOSITE PRINT TO REPRODUCE FROM THE SUPERIMPOSED PRINTS SAID COMPOSITE DESIGN, AND REPRODUCING SAID LAST MENTIONED COMPOSITE DESIGN ON A LIGHT SENSITIVE PLATE PHOTO-MECHANICALLY. 